The insulin-like growth factors, also known as somatomedins, include insulin-like growth factor-I (IGF-I) and insulin-like growth factor-II (IGF-II) (Klapper, et al., (1983) Endocrinol. 112:2215 and Rinderknecht, et al., (1978) Febs.Lett. 89:283). These growth factors exert mitogenic activity on various cell types, including tumor cells (Macaulay, (1992) Br. J. Cancer 65:311), by binding to a common receptor named the insulin-like growth factor receptor-1 (IGFR1) (Sepp-Lorenzino, (1998) Breast Cancer Research and Treatment 47:235). Interaction of IGFs with IGFR1 activates the receptor by triggering autophosphorylation of the receptor on tyrosine residues (Butler, et al., (1998) Comparative Biochemistry and Physiology 121:19). Once activated, IGFR1, in turn, phosphorylates intracellular targets to activate cellular signaling pathways. This receptor activation is critical for stimulation of tumor cell growth and survival. Therefore, inhibition of IGFR1 activity represents a valuable potential method to treat or prevent growth of human cancers and other proliferative diseases.
Several lines of evidence indicate that IGF-I, IGF-II and their receptor IGFR1 are important mediators of the malignant phenotype. Plasma levels of IGF-I have been found to be the strongest predictor of prostate cancer risk (Chan, et al., (1998) Science 279:563) and similar epidemiological studies strongly link plasma IGF-I levels with breast, colon and lung cancer risk.
Overexpression of Insulin-like Growth Factor Receptor-I has also been demonstrated in several cancer cell lines and tumor tissues. IGFR1 is overexpressed in 40% of all breast cancer cell lines (Pandini, et al., (1999) Cancer Res. 5:1935) and in 15% of lung cancer cell lines. In breast cancer tumor tissue, IGFR1 is overexpressed 6–14 fold and IGFR1 exhibits 2–4 fold higher kinase activity as compared to normal tissue (Webster, et al., (1996) Cancer Res. 56:2781 and Pekonen, et al., (1998) Cancer Res. 48:1343). Ninety percent of colorectal cancer tissue biopsies exhibit elevated IGFR1 levels wherein the extent of IGFR1 expression is correlated with the severity of the disease. Analysis of primary cervical cancer cell cultures and cervical cancer cell lines revealed 3-and 5-fold overexpression of IGFR1, respectively, as compared to normal ectocervical cells (Steller, et al., (1996) Cancer Res. 56:1762). Expression of IGFR1 in synovial sarcoma cells also correlated with an aggressive phenotype (i.e., metastasis and high rate of proliferation; Xie, et al., (1999) Cancer Res. 59:3588).
Acromegaly, a slowly developing disease, is caused by hypersecretion of growth hormone and IGF-I (Ben-Schlomo, et al., (2001) Endocrin. Metab.Clin. North. Am. 30:565–583). Antagonism of IGFR1 function may be helpful in treating the disease.
There are several antibodies, which are known in the art, which inhibit the activity of IGFR1. However, these are of relatively low therapeutic value. For example, α-IR3 (Kull, et al., (1983) J. Biol. Chem. 258:6561), 1H7. (Li et al., (1993) Biochem. Biophys. Res. Comm. 196.92–98 and Xiong et al., (1992) Proc. Natl. Acad. Sci., U.S.A. 89:5356–5360; Santa Cruz biotechnology, Inc.; Santa Cruz, Calif.) and MAB391 (R&D Systems; Minneapolis, Minn.) are mouse monoclonal antibodies which interact with IGFR1 and inhibit its activity. Since these are mouse antibodies, their therapeutic utility in humans is limited. When immunocompetent human subjects are administered a dose of mouse antibodies, the subjects produce antibodies against the mouse immunoglobulin sequences. These human anti-mouse antibodies (HAMA) neutralize the therapeutic antibodies and may induce acute toxicity (i.e., a HAMA response).
One method by which to avert a HAMA response is through the use of fully-human antibodies which lack any foreign (e.g., mouse) amino acid sequences. Although the use of fully-human antibodies is an effective method by which to reduce or prevent human host immune rejection of the therapeutic antibody, rejection of the fully-human antibody can occur. Human rejection of human antibodies may be referred to as a human anti-human antibody response (HAHA response). HAHA response can be mediated by factors such as the presence of rare, low occurrence amino acid sequences in the fully-human antibodies. For this reason, therapeutic antibodies may also be optimized by the inclusion of non-immunogenic or only weakly immunogenic human antibody framework sequences. Preferably, the sequences occur frequently in other human antibodies.